Hairpin winding electric machine with multi-conductor hairpin assemblies

ABSTRACT

An electric machine includes a stator core defining slots and a first hairpin assembly installed in the stator core. The first hairpin assembly includes first and second same hairpins, each having first and second ends and separately coated to have first and second outer coating surfaces, respectively. The hairpin assembly is in first and second ones of the slots such that the first and second outer surfaces are touching. A weld material joins the first ends and another weld material joins the second ends.

TECHNICAL FIELD

The present disclosure relates to electric machines and morespecifically to electric machines that include hairpin windings formedof multi-conductor hairpin assemblies. This disclosure also relates tomethods of manufacturing electric machines that include multi-conductorhairpin assemblies.

BACKGROUND

Vehicles such as battery-electric vehicles and hybrid-electric vehiclescontain a traction-battery assembly to act as an energy source for thevehicle. The traction battery may include components and systems toassist in managing vehicle performance and operations. The tractionbattery may also include high-voltage components, and an air or liquidthermal-management system to control the temperature of the battery. Thetraction battery is electrically connected to an electric machine thatprovides torque to driven wheels. Electric machines typically include astator and a rotor that cooperate to convert electrical energy intomechanical motion or vice versa.

SUMMARY

According to one embodiment, an electric machine includes a stator coredefining slots and a first hairpin assembly installed in the statorcore. The first hairpin assembly includes first and second samehairpins, each having first and second ends and separately coated tohave first and second outer coating surfaces, respectively. The hairpinassembly is in first and second ones of the slots such that the firstand second outer surfaces are touching. A weld material joins the firstends and another weld material joins the second ends.

According to another embodiment, a method of assembling a hairpin motorincludes separately forming first and second hairpins to each have firstand second legs and inserting the first legs in a first stator slot andthe second legs in a second stator slot. The method further includesbending the first legs of each hairpin to form first twists and joiningends of the first twists together.

According to yet another embodiment, a method of assembling a hairpinmotor includes providing separate first, second, third, and fourthhairpin blanks having separate insulation coatings and no commonencasement, and bending each of the blanks to form first, second, third,and fourth hairpins each having first and second legs. The methodfurther includes assembling the first and second hairpins on a statorcore by inserting the first and second legs of the first and secondhairpins into first and second slots of the stator core, respectively.The method also includes assembling the third and fourth hairpins on thestator core by inserting the first and second legs of the third andfourth hairpins into third and fourth slots of the stator core,respectively, and welding the first legs of the first and secondhairpins to each other and to the second legs of the third and fourthhairpins so that the first, second, third, and fourth hairpins areelectrically connected to each other via a weld.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an electric machine.

FIG. 2 is a perspective view of a stator of the electric machine.

FIG. 3 is a perspective view of a hairpin assembly prior to installationin the stator.

FIG. 4 is a magnified side view of the hairpin assembly of FIG. 3 neararea 4-4.

FIG. 5A is a cross-sectional end view of a stator slot with the hairpinassemblies installed.

FIG. 5B is a cross-sectional end view of a stator slot with the hairpinassemblies according to an alternative embodiment.

FIG. 5C is a cross-sectional end view of a stator slot with the hairpinassemblies according to another alternative embodiment.

FIG. 6 is a flow chart illustrating a method of assembling an electricmachine having hairpin assemblies.

FIG. 7 is a perspective view of a hairpin blank.

FIG. 8 is a front view of a pair of hairpins formed from the hairpinblanks prior to installation in a stator core.

FIG. 9 is a schematic diagram of a portion of a stator core with hairpinassemblies of one path installed in corresponding stator slots.

FIG. 10 is a detail view of a weld connecting a pair of hairpinsassemblies together.

FIG. 11 is a perspective view of a hairpin assembly having threehairpins.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described herein. It is to beunderstood, however, that the disclosed embodiments are merely examplesand other embodiments can take various and alternative forms. Thefigures are not necessarily to scale; some features could be exaggeratedor minimized to show details of particular components. Therefore,specific structural and functional details disclosed herein are not tobe interpreted as limiting, but merely as a representative basis forteaching one skilled in the art to variously employ the presentinvention. As those of ordinary skill in the art will understand,various features illustrated and described with reference to any one ofthe figures can be combined with features illustrated in one or moreother figures to produce embodiments that are not explicitly illustratedor described. The combinations of features illustrated providerepresentative embodiments for typical applications. Variouscombinations and modifications of the features consistent with theteachings of this disclosure, however, could be desired for particularapplications or implementations.

Referring to FIG. 1, an electric machine 20 may be used in a vehiclesuch as a fully electric vehicle or a hybrid-electric vehicle. Theelectric machine 20 may be referred to as an electric motor, a tractionmotor, a generator, or the like. The electric machine 20 may be apermanent magnet machine, an induction machine, or the like. In theillustrated embodiment, the electric machine 20 is a three-phasealternating current (AC) machine. The electric machine 20 is capable ofacting as both a motor to propel the vehicle and as a generator such asduring regenerative braking.

The electric machine 20 may be powered by a traction battery of thevehicle. The traction battery may provide a high-voltage direct current(DC) output from one or more battery-cell arrays, sometimes referred toas battery-cell stacks, within the traction battery. The battery-cellarrays may include one or more battery cells that convert storedchemical energy to electrical energy. The cells may include a housing, apositive electrode (cathode), and a negative electrode (anode). Anelectrolyte allows ions to move between the anode and cathode duringdischarge, and then return during recharge. Terminals allow current toflow out of the cells for use by the vehicle.

The traction battery may be electrically connected to one or more powerelectronics modules. The power electronics modules may be electricallyconnected to the electric machines 20 and may provide the ability tobi-directionally transfer electrical energy between the traction batteryand the electric machine 20. For example, a typical traction battery mayprovide a DC voltage while the electric machine 20 may require athree-phase AC voltage. The power electronics module may include aninverter that converts the DC voltage to a three-phase AC voltage asrequired by the electric machine 20. In a regenerative mode, the powerelectronics module may convert the three-phase AC voltage from theelectric machine 20 acting as a generator to the DC voltage required bythe traction battery. While described in the context of an electrifiedvehicle, the electric machine 20 may also be used in nonautomotiveapplications. For example, the electric machine 20 may be used inmanufacturing equipment or in power-generation machines.

Referring to FIGS. 1 and 2, the electric machine 20 includes a housing21 that encloses the stator 22 and the rotor 24. The stator 22 is fixedto the housing 21 and includes a cylindrical core 32 having an innerdiameter 28 that defines a hole 30 and an outer diameter 29. The core 32may be formed from a plurality of stacked laminations 33. The rotor 24is supported for rotation within the hole 30. The rotor 24 may includewindings or permanent magnets that interact with windings of the stator22 to generate rotation of the rotor 24 when the electric machine 20 isenergized. The rotor 24 may be supported on a driveshaft 26 that extendsthrough the housing 21. The driveshaft 26 is configured to couple with aload, such as a drivetrain of the vehicle.

The stator core 32 defines stator slots 34 circumferentially arrangedand extending outwardly from the inner diameter 28. The slots 34 may beequally spaced around the circumference and extend axially from a firstend 36 of the core 32 to a second end 38. In the illustrated embodiment,the core 32 defines forty-eight slots and has eight poles, but the core32 may include more or fewer slots and/or poles in other embodiments.For example, the core 32 may define seventy-two slots and have eightpoles.

The slots 34 are spaced by a circumferential distance measured betweenthe center lines of two adjacent stator slots. This distance can be usedas a unit of distance (hereinafter “a slot”) for relating and measuringother components of the stator 22. The distance unit “slot” is sometimesreferred to as “slot pitch” or “slot span.”

The electric machine 20 may include hairpin windings 40 placed in theslots 34 of the core 32. Hairpin windings are an emerging technologythat improves efficiency for electric machines used in vehicles andother contexts. The hairpin windings 40 improve efficiency by providinga greater amount of stator conductors to reduce resistance of thewinding 40 without encroaching into space reserved for the electricalsteel and the magnetic flux path. The hairpin windings 40 may be wavewindings in which the windings 40 weave pole to pole in a wave-likepattern.

The electric machine 20 may be a three-phase AC machine in which thehairpin windings 40 are arranged in a U phase, a V phase, and a W phase.Each phase includes associated conductors (also known as pins, hairpins,or bar conductors) arranged in two parallel paths of windings in theillustrated embodiment. Each phase may include more or less parallelpaths in other embodiments.

The hairpins are generally U-shaped and include a pair of legs joined bya crown. The hairpins are installed in the stator core 32 by insertingthe legs through corresponding ones of the slots 34. All of the hairpinsmay be installed from the same end of the stator core 32, e.g., end 36,so that all of the crowns are located on one end of the stator, e.g.,end 36, and the ends of the legs are located on the other end, e.g., end38. Once installed, the legs of the hairpins are bent away from eachother to form twists that connect with the twists of other hairpins. Theends of corresponding hairpins are joined by a connection such as a weld48. The connections may be arranged in rows such as weld rows 62. End 36may be referred to as the crown end and end 38 may be referred to as theweld end. Each path includes associated hairpins that are connected atends of the twists to form a continuous conductor between a terminal anda neutral connection.

Traditionally, each hairpin consisted of a single, solid bar conductor,e.g., copper, bent into a desired shape. These hairpins had a relativelylarge cross-sectional area, which produced increased AC loss. AC loss ina conductor can be reduced by decreasing the cross-sectional area ofindividual conductors. That is, replacing a single bar conductor withtwo or more smaller conductors connected in parallel reduces AC loss andimproves performance of the electric machine. This disclosure proposesto replace the traditional single bar hairpins with hairpin assembliesthat include two or more hairpins connected in parallel. Each hairpin ofthe hairpins assemblies are connected at the ends and are electricallyisolated in the middle by separate coatings of the hairpins.

The U phase may include hairpin assemblies 42 a that are connected toeach other to form a first path 44, and hairpin assemblies 42 b that areconnected to each other to form a second path 46. Each of the pathsincludes a first end that starts at the terminal 50 and a second endthat ends at a neutral connection 52. The paths 44, 46 are connected toeach other at the terminal 50 and at the neutral connection 52 but areotherwise electrically isolated from each other. Each of the pathsencircles the stator core 32 by weaving in and out of select ones of theslots 34. Each hairpin assembly includes two or more separately formedhairpins that are connected in parallel at the ends of the hairpins.(Note: FIG. 2 shows the hairpin assemblies schematically as a singlesolid object for illustrative purposes only; in actuality, each hairpinassembly includes multiple hairpins. This will be shown in detailbelow.)

The V phase may include a plurality of hairpin assemblies 56 a and 56 bthat are interconnected to form a first path 58 and a second path 60,respectively. Each of the paths includes a first end that starts at aterminal 64 and a second end that ends at the neutral connection 52. Thepaths 58, 60 are connected to each other at the terminal 64 and at theneutral connection 52 but are otherwise electrically isolated from eachother. Each of the paths encircles the stator core 32 by weaving in andout of select ones of the slots 34.

The W phase may include a plurality of hairpin assemblies 70 a and 70 bthat are interconnected to form a first path 72 and a second path 74,respectively. Each of the paths includes a first end that starts at aterminal 78 and a second end that ends at the neutral connection 52. Theneutral connection may be a single neutral connection, e.g., a singlestrip of metal, used to connect all six paths, or multiple neutralconnections may be used. The paths 72, 74 are connected to each other atthe terminal 78 and at the neutral connection 52 but are otherwiseelectrically isolated from each other. Each of the paths 72, 74encircles the stator core 32 by weaving in and out of select ones of theslots 34. The terminals 50, 64, 78 may be connected to the inverter andreceive voltage from the inverter, which creates torque-producingcurrent in the winding paths causing the rotor 24 to rotate within thestator 22.

The following figures and related text describe example hairpinassemblies that may be used in conjunction with the electric machine 20or other electric machines that include hairpin windings.

Referring to FIGS. 3 and 4, an example hairpin assembly 100 (shown in apreinstalled position) includes a first hairpin 102 and a second hairpin104 which are bent into the shape shown. The first hairpin 102 includesa crown 106 having a pair of angled segments 108, 110 that meet at avertex 112. A first leg 114 extends from the angled segment 108 and asecond leg 116 extends from the angled segment 110. The first and secondlegs are separated by a span of slots. The first hairpin 102 includes acoating 118 to electrically insulate the hairpin. The coating 118 isstripped away at the ends 120 and 122 so that the hairpin can beelectrically connected to other hairpins. The second hairpin 104 alsoincludes a crown having a pair of angled segments that meet at a vertex.A first leg 124 extends from one of the angled segments, and a secondleg 126 extends from the other angled segment. The second hairpin 104includes a coating 128 to electrically insulate the hairpin. The coating128 is stripped away at the ends 130 and 132. The first and secondhairpins 102 and 104 have their own insulating layer, i.e. the coatings118 and 128, and do not have a common encasement or insulation. Thisallows the individual hairpins 102 and 104 to be separately formed, moverelative to each other, and to be installed one at a time if so desired.In the illustrated embodiment, the hairpin assembly 100 has a span ofsix slots between the legs, but this span may be different in otherembodiments. In some electric machines, there may be different types ofthe hairpin assemblies that have different shapes and/or different slotspans.

The first and second hairpins 102, 104 may be designed to have the sameshape or may have different shapes. In this context “same shape” refersto design shape and contemplates minor differences due to manufacturinglimitations. The first and second hairpins may be bent separately or maybe stacked together and bent together into the shape shown in FIG. 3.The first and second hairpins 102, 104 may be installed into the statorslots separately or may be aligned with each other and installedtogether. The first and second hairpins may be connected to the endsprior to installation in the stator core or may be connected at the endsduring the welding process that connected the hairpins to form thewindings. This flexibility of fabrication and installation is providedby not having a common encasement for the hairpin assembly.

Referring to FIG. 5A, each slot 34 includes slot positions sequentiallynumbered from the inner diameter 28 towards the outer diameter 29. Theslots 34 may include an inner radial layer 140 of pins, a middle radiallayer 142 of pins, and an outer radial layer 144 of pins. Each of thelayers may include at least two radial positions that are adjacent toeach other. In the illustrated embodiment, each slot 34 has sixsequential positions in a one-by-six linear arrangement. The firstposition is near the inner diameter 28 of the stator core 32 and thesixth position is near the outer diameter 29 of the stator core 32. Theinner layer 140 includes the first and second positions; the middlelayer 142 includes the third and fourth positions; and the outer layer144 includes the fifth and sixth positions.

Each slot position is sized to receive the entire hairpin assembly. Inthe illustrated embodiment, each slot position is sized to receive apair of hairpins, such as hairpins 102 and 104. In FIG. 5A, the hairpins102 and 104 of the hairpin assemblies 100 are arranged radially placingthe hairpins in a one-by-twelve arrangement. But, in other embodiments,as shown in FIG. 5B, the hairpins 102 and 104 may be side-by-side, i.e.,adjacent in the circumferential direction of the stator core, in atwo-by-six arrangement for example. In yet other embodiments, as shownin FIG. 5C, the hairpins 105 may be side-by-side and arranged radiallyso that each hairpin assembly 107 includes four hairpins 105. Of course,in other embodiments, each hairpin assembly may include more or lesshairpins. The hairpin assemblies of the various phases are positioned inthe slots to form a desired winding arrangement. In some embodiments,each slot may only include hairpins of one of the phases, but in otherembodiments, each slot may include more than one phase. Many types ofwinding arrangements are possible; the hairpin assemblies of thisdisclosure are compatible with many types of winding arrangements andthis disclosure is not limited to any particular winding arrangement.

The following figures and associated text describe methods ofmanufacturing hairpin assemblies and assembling electric machines thathave hairpin assemblies.

Referring to FIG. 7, the method 200 begins at operation 202 wherehairpin blanks (also known as bar conductors) 220 are provided. Thehairpins may begin as straight blanks that include a bar conductor 222encased in an insulation coating 224. The bar conductors 222 are formedof an electrically conductive material such as copper, gold, silver, andthe like. The blanks 220 may be provided in precut strips of a desiredlength or may come as a coil that must be cut into blanks of a desiredlength. Once the blanks 220 are of the desired length, the ends arestripped (if not already done) to expose the bar conductor 222.

Referring to FIG. 8, the blanks 220 are bent to form a plurality ofhairpins 226 that each include a crown 228 and a pair of straight legs230, 232 at step 204. Corresponding ones of the hairpins 226 will begrouped into hairpin assemblies. The blanks 220 of common hairpinassemblies may be bent to have the same shape or may have slightlydifferent shapes. The hairpins 226 may be the same or similar tohairpins 102/104 described above.

Once the hairpins 226 are formed into the shape shown in FIG. 8, thehairpins 226 may be arranged in groups of hairpin assemblies that arethen inserted into select slots of the stator core 32 at operation 206.The hairpins of a hairpin assembly may or may not be joined to eachother prior to installation. Alternatively, the hairpins of each hairpinassembly may be inserted individually. For example, for each hairpinassembly, the first hairpin is inserted into first and second ones ofthe stator slots first and, subsequently, the second hairpin is insertedinto the first and second stator slots. The legs of hairpins belongingto a same hairpin assembly are inserted into same slot positions suchthat outer surfaces of the coatings 224 touch each other.

FIG. 9 illustrates three hairpin assemblies 240 a, 240 b, and 240 cinserted into the slots 34 of the stator core 32. In this example, thehairpin assemblies have a span of six slots and each includes first andsecond hairpins as described above with regards to hairpin assemblies100. Hairpin assembly 240 a has first and second legs disposed in slot 1and slot 6, respectively; hairpin assembly 240 b has first and secondlegs disposed in slot 12 and slot 18, respectively; and hairpin assembly240 c has first and second legs disposed in slot 24 and slot 30,respectively. At step 208, the legs 230, 232 of the hairpins are bent toform twists 242 and 244. Each of the twists may have a span that isequal to one half of the span of the hairpins, which in this case isthree slots, but this need not always be the case and the twist may belonger or shorter in other embodiments. The twists 242 and 244 may bebend in substantially opposite circumferential directions so that thehairpin assemblies can be joined to other hairpin assemblies. Someelectric machines may include special hairpins in which the twistsextend in a same direction. The associated legs of each hairpin assembly240 may be bent separately or together to form the twists 242, 244. Onceall of the hairpins are assembled into the stator core 32 and the twistsare formed, corresponding ones of the hairpin assemblies are joined toeach other at operation 210. The hairpin assemblies may be joined bywelding (e.g., laser welding), soldering, brazing, and the like.

In FIG. 9, the first twists 242 b of assembly 240 b is joined to thesecond twists 244 a of assembly 240 a by a weld 246, and the secondtwists 244 b of assembly 240 b is joined to the first twists 242 c ofthe assembly 240 c by a weld 248. The weld assemblies 240 a, 240 b, and240 c are electrically connected in series and form a portion of one ofthe paths.

FIG. 10 illustrates a detail view of the weld 246. In this embodiment,the hairpins of the hairpin assembly were not joined prior to insertion.The first legs 250, 252 of the hairpin assembly 240 a are joinedtogether by the weld 246 and are joined to the second legs 254, 256 ofthe hairpin assembly 240 b by the weld 246. The weld 246 also joins thelegs 254 and 256 to each other. The remaining welds such as weld 248 mayhave a similar structure. The weld 246 may be formed in a single weldingoperation. In other embodiments, the legs 250 and 252 and the legs 254and 256 may be joined by a first and second welds prior to installationof the hairpin assemblies in the stator core. Here, the weld 246 is usedto join the hairpin assemblies 240 a and 240 b to each other.

After welding, the ends of the hairpin assemblies 240 are electricallyconnected to each other to form a pair of parallel paths that areelectrically isolated from each other, except at the welds, by theinsulation coatings. The conductors of the parallel paths have a reducedcross-sectional area, which decreases the AC losses as compared to asingle bar conductor having a cross-sectional area that is equal to thesum of the multiple conductors of hairpin assemblies 240.

The stator may be dipped in varnish or epoxy at step 212 after thewindings are completed to coat the stator core and windings to provideadditional insulation and add stiffness to the windings. Once the statoris assembled, the rotor may be installed into the stator at step 214.The method 200 is not an exhaustive list of all steps involved inmanufacturing an electric machine. Additionally, this disclosure is notlimited to the above-described sequence of steps. Some of the steps maybe reordered, modified or omitted in some embodiments.

Referring to FIG. 11, the hairpins assemblies may have more than twohairpins. For example, FIG. 11 shows a hairpins assembly 280 thatincludes three hairpins 282, 284, 286. The three hairpins may be formedfrom individual blanks that are bent to form hairpins in the shapeshown. Each of the hairpins has a coating 288 that electricallyinsulates the hairpins from each other. Similar to above, the ends 290of the hairpins 282, 284, and 286 are joined at the ends 290 by welds toplace the three hairpins in parallel. It is possible for the hairpinsassemblies to have four or more hairpins in other embodiments, butinstalling and welding the hairpins may become more difficult as thenumber of hairpins increases reducing the benefit of having additionalhairpins in the hairpin assemblies.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms encompassed by the claims.The words used in the specification are words of description rather thanlimitation, and it is understood that various changes can be madewithout departing from the spirit and scope of the disclosure. Aspreviously described, the features of various embodiments can becombined to form further embodiments of the invention that may not beexplicitly described or illustrated. While various embodiments couldhave been described as providing advantages or being preferred overother embodiments or prior art implementations with respect to one ormore desired characteristics, those of ordinary skill in the artrecognize that one or more features or characteristics can becompromised to achieve desired overall system attributes, which dependon the specific application and implementation. These attributes caninclude, but are not limited to cost, strength, durability, life cyclecost, marketability, appearance, packaging, size, serviceability,weight, manufacturability, ease of assembly, etc. As such, embodimentsdescribed as less desirable than other embodiments or prior artimplementations with respect to one or more characteristics are notoutside the scope of the disclosure and can be desirable for particularapplications.

What is claimed is:
 1. A method of assembling a hairpin motorcomprising: providing separate first, second, third, and fourth hairpinblanks having separate insulation coatings and no common encasement;bending each of the hairpin blanks to form first, second, third, andfourth hairpins each having first and second legs; assembling the firstand second hairpins on a stator core by inserting the first and secondlegs of the first and second hairpins into first and second slots of thestator core, respectively; assembling the third and fourth hairpins onthe stator core by inserting the first and second legs of the third andfourth hairpins into third and fourth slots of the stator core,respectively; and welding the first legs of the first and secondhairpins to each other and to the second legs of the third and fourthhairpins so that the first, second, third, and fourth hairpins areelectrically connected to each other via a weld.
 2. The method of claim1 further comprising: providing separate fifth and sixth hairpin blankshaving separate insulation coatings and no common encasement; bendingthe fifth and sixth hairpin blanks to form fifth and sixth hairpins eachhaving first and second legs; assembling the fifth and sixth hairpins onthe stator core by inserting the first and second legs of the fifth andsixth hairpins into fifth and sixth slots of the stator core,respectively; and welding the first legs of the fifth and sixth hairpinsto each other and to the second legs of the first and second hairpins sothat the first, second, fifth, and sixth hairpins are electricallyconnected to each other via another weld.
 3. The method of claim 1further comprising: providing a fifth hairpin blank having an insulationcoating; bending the fifth hairpin blank to have first and second legs;and assembling the fifth hairpin on the stator core by inserting thefirst and second legs of the fifth hairpin into the first and secondslots of the stator core, respectively, wherein the welding joins thefifth hairpin to the first and second hairpins.
 4. The method of claim1, wherein the first and second hairpins are bent separately.
 5. Themethod of claim 1 further comprising inserting a rotor into the statorcore.
 6. A method of assembling a hairpin motor comprising: providing astator core having first, second, third and fourth slots; providingseparate first, second, third, and fourth hairpin blanks having separateinsulation coatings and no common encasement; bending each of thehairpin blanks to form first, second, third, and fourth hairpins eachhaving first and second legs; assembling the first and second hairpinson a stator core by inserting the first and second legs of the first andsecond hairpins into the first and second slots of the stator core,respectively; assembling the third and fourth hairpins on the statorcore by inserting the first and second legs of the third and fourthhairpins into the third and fourth slots of the stator core,respectively; welding the first legs of the first and second hairpins toeach other and to the second legs of the third and fourth hairpins sothat the first, second, third, and fourth hairpins are electricallyconnected to each other via a weld; providing separate fifth and sixthhairpin blanks having separate insulation coatings and no commonencasement; bending the fifth and sixth hairpin blanks to form fifth andsixth hairpins each having first and second legs; assembling the fifthand sixth hairpins on the stator core by inserting the first and secondlegs of the fifth and sixth hairpins into fifth and sixth slots of thestator core, respectively; and welding the first legs of the fifth andsixth hairpins to each other and to the second legs of the first andsecond hairpins so that the first, second, fifth, and sixth hairpins areelectrically connected to each other via another weld.
 7. The method ofclaim 6 further comprising: providing a fifth hairpin blank having aninsulation coating; bending the fifth hairpin blank to have first andsecond legs; and assembling the fifth hairpin on the stator core byinserting the first and second legs of the fifth hairpin into the firstand second slots of the stator core, respectively, wherein the weldingjoins the fifth hairpin to the first and second hairpins.
 8. The methodof claim 6, wherein the first and second hairpins are bent separately.9. The method of claim 6 further comprising inserting a rotor into thestator core.